In recent years, instead of bulk piezoelectric material, the utilization of piezoelectric elements using piezoelectric thin films has been well developed. For example, the piezoelectric sensors, e.g., gyro sensors, pressure sensors, pulse sensors, shock sensors and microphones, have been developed by using the piezoelectric effect that converts the force applied to the piezoelectric thin film into a voltage. In addition, piezoelectric actuators, e.g., the head assembly in a hard-disk drive and the head in an ink jet printer, have been developed by using the inverse piezoelectric effect which makes the piezoelectric thin film deformed when a voltage is applied to the piezoelectric thin film. Further, buzzers, resonators and the like are also the examples which use the inverse piezoelectric effect.
If the piezoelectric material is made as a thin film, it is possible to downsize the element so that it can be applied broadly into various technical fields. Meanwhile, the productivity can be improved since a plurality of elements can be integratedly formed on a substrate, In addition, there are also advantages in terms of performance such as the sensitivity is improved when the sensor is formed using the piezoelectric thin film.
The piezoelectric thin film, which is used to form a piezoelectric thin film element, is prepared by a film formation method such as sputtering or chemical vapor deposition (CVD). However, during the film formation, oxygen defect will occur in the piezoelectric thin film and the defects in structure will heavily affect the piezoelectric properties.
Patent Document 1 discloses that the piezoelectric properties can be improved by controlling the crystal structure at the interface between the electrode layer and the piezoelectric thin film since the oxygen defect occurs easily at this interface, and further forming a piezoelectric thin film with a subtle state change in the crystal structure in the film thickness direction.